By-elections to Natham and Thiruvattar constituencies were held in Tamil Nadu, India, on 5 and 11 September 1999 respectively.

Elections for three state assembly constituencies, Nellikuppam, Tiruchirappalli - II and Arantangi were held on 17 February 2000.

In the first phase, TMC lost a seat to AIADMK and Dravida Munnetra Kazhagam (DMK) lost a seat to Communist Party of India (Marxist) (CPI (M)).

In the second phase, AIADMK splinter party MADMK, was able to pick up a seat from AIADMK and DMK was able to hold on to its seats.

Source: Tamil Nadu Legislative Assembly[3] 1.